Wireless communication systems are widely deployed in order to provide various kinds of communication services, such as voice and data. In general, the wireless communication systems are multiple access systems which can share available system resources (e.g., bandwidths and transmission power) and support communication with multiple users. The multiple access systems may include, for example, a CDMA (code division multiple access) system, a FDMA (frequency division multiple access) system, a TDMA (time division multiple access) system, an OFDMA (orthogonal frequency division multiple access) system, and an SC-FDMA (single carrier frequency division multiple access) system.
In a common wireless communication system, although the bandwidth of uplink and the bandwidth of downlink are differently set, only one carrier is chiefly taken into consideration. The carrier is defined by a center frequency and a bandwidth. A multi-carrier system uses a plurality of carriers having a bandwidth smaller than the entire bandwidth.
LTE (long term evolution) based on 3GPP (3rd Generation Partnership Project) TS (Technical Specification) Release 8 is the leading next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.5.0 (2008-12) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, physical channels in LTE may be divided into a PDSCH (Physical Downlink Shared Channel) and a PUSCH (Physical Uplink Shared Channel) which are data channels and a PDCCH (Physical Downlink Control Channel), a PCFICH (Physical Control Format Indicator Channel), a PHICH (Physical Hybrid-ARQ Indicator Channel), and a PUCCH (Physical Uplink Control Channel) which are control channels.
A 3GPP LTE system supports only one (i.e., one carrier) of {1.4, 3, 5, 10, 15, and 20} MHz bandwidths. A multi-carrier system may use two carriers, each having a 20 MHz bandwidth, or three carriers having a 20 MHz bandwidth, a 15 MHz bandwidth, and a 5 MHz bandwidth, respectively, in order to support the entire 40 MHz bandwidth.
A multi-carrier system has advantages in that it can support backward compatibility with the existing system and also increase the data rate through multiple carriers.
In a single carrier system, control channels and data channels are designed based on a single carrier. In a multi-carrier system, however, it may be inefficient if the channel structure of the single carrier system is used without change.
A CQI (Channel Quality Indicator) indicates a channel condition. The CQI is used in order for a base station to schedule UEs within a cell. In order to schedule each of carriers in a multi-carrier system, a CQI is necessary for each carrier. If CQIs for all the carriers are reported, however, radio resources may be inefficiently used.
It is required a method and apparatus capable of reporting a CQI in a multi-carrier system.